Reptilian Tooth and Jaw Development

爬行动物和哺乳动物有着共同的祖先，可以追溯到3亿多年前，但在进化过程中，头骨和牙齿出现了显着的特化。我们的目标是确定这些差异是如何以及何时在开发中出现的。例如，大多数爬行动物的头骨比哺乳动物有更多的开口。哺乳动物总是有封闭的腭，将口腔和鼻腔分开。与此相反，蛇、蜥蜴和鸟类的上颚是张开的，海龟的上颚是原始的，而令人惊讶的是，短吻鳄的上颚像哺乳动物一样是闭合的。在牙列中，牙齿解剖结构和替换能力也有显着差异。大多数蛇，蜥蜴和鳄鱼在一生中不断更换牙齿（多齿），而哺乳动物只能更换一次牙齿。 爬行动物和哺乳动物的胚胎在早期阶段非常相似，反映了它们共同的起源。在发育的关键阶段，将在海龟、蜥蜴、鸟类和短吻鳄中检查涉及头骨和腭发育的基因，以确定与后来的头骨解剖结构相关的细微差异。还将分析头部和腭部的形状，以在可以检测到形态差异时精确测量。为了测试关键基因的功能，将逆转录病毒放入鸡体内，以改变基因表达，使其类似于非鸟类爬行动物。我们假设其中一些基因会将鸟类的解剖结构转换为其他爬行动物的解剖结构。 我们将在对豹纹壁虎的纵向研究中调查牙齿替换，以及收集到的关于鬣蜥的历史数据。我们将测试是否有全球性的线索，调节牙齿更换的时间和模式，以及这些是否在孵化前建立。我们还将通过拔牙、在牙齿旁边注射化学物质或损坏牙齿替换装置来测试环境对牙齿替换的作用。每周进行蜡咬，以记录牙齿脱落情况。我们还将注射一种荧光染料，在实验进行时将其掺入矿化牙齿中。将用荧光显微镜记录荧光牙齿随时间的脱落和萌出。后续实验将分析固定组织的基因表达和细胞增殖变化。UBC的爬行动物研究小组在加拿大和世界上都是独一无二的。我们对头骨和牙齿的分子进化的创新研究将为动物如何适应环境变化提供见解。我们的研究结果引起了古生物学家、发育生物学家和广大科学界的极大兴趣。

Reptiles and mammals share a common ancestor dating back more than 300 million years but during evolution significant specializations in the skull and teeth have arisen. Our goal is to determine how and when in development these differences arose. For example, skulls of the majority of reptiles have more openings than mammals. Mammals always have closed palates that separate the oral and nasal cavities. In contrast snakes, lizards and birds have open palates, turtles have a primitive palate and surprisingly alligators have a closed palate like mammals. In the dentition, there are also striking differences in tooth anatomy and replacement capacity. Most snakes, lizards and crocodilians replace their teeth continuously throughout life (polyphyodonty), whereas mammals can only replace their teeth once. The embryos of reptiles and mammals are remarkably similar at early stages reflecting their common origins. At key stages of development genes involved in skull and palate development will be examined in turtles, lizards, birds and alligators to determine subtle differences that correlate with later skull anatomy. The shape of the head and palate will also be analyzed to measure precisely when differences in morphology can be detected. To test the function of key genes, retroviruses will be placed into the chicken to change gene expression to resemble that of non-avian reptiles. We hypothesize that some of these genes will convert the bird anatomy into that of other reptiles. We will investigate tooth replacement in longitudinal studies on leopard geckos as well as historical data collected on iguanas. We will test whether there are global cues that regulate the timing and pattern of tooth replacement and whether these are set up prior to hatching. We will also test the role of the environment on tooth replacement by removing teeth, injecting chemicals next to the teeth or injuring the tooth replacement apparatus. Wax bites will be taken weekly to record the shedding of teeth. We will also inject a fluorescent dye that is incorporated into mineralizing teeth at the time the experiments are conducted. The shedding and eruption of fluorescent teeth over time will be recorded with a fluorescence microscope. Follow-up experiments will analyze the fixed tissues for gene expression and cell proliferation changes. The reptile research group at UBC is unique in Canada and the world. Our innovative studies on molecular evolution of the skull and teeth will provide the insights into how animals adapted to environmental changes. Our results are of great interest to paleobiologists, developmental biologists and the broad scientific community.